Electric motor drives are becoming more prevalent in automotive systems every year. As hybrid and electric vehicles become more popular, the quantity of automotive AC drive systems in the field will grow rapidly. They can be used in either electric or hybrid vehicles as a part the propulsion system. In a typical application, the motor drive requires a position or speed sensor device to properly control the motor. Fault tolerance and robustness are important features to insure trouble-free operation of the vehicle. In a typical drive system, failure of the position/speed sensor will cause a loss of propulsion fault. This would leave the driver stranded with no means of moving the vehicle.
Most fault detection and fault tolerant approaches focus on faults of power semiconductors in an inverter and motor windings. In one approach, sensor faults of an induction motor drive system are identified and the control system is reconfigured according to the specific fault of the sensor. The control system tolerates the faults by changing the control algorithm from a high performance indirect vector control to a simple volts/hertz (V/Hz) control. As a result, the traction system of the vehicle provides gracefully degraded performance according to the faults.
In “Fault Tolerant Operation of Induction Motor Drives With Automatic Controller Reconfiguration”, Sepe, R. B., Jr., Fahimi, B., Morrison, C., and Miller, J. M., Electric Machines and Drives Conference, 2001, IEMDC 2001. IEEE International, 2001, pages 156–162, a fault tolerant drive system for asynchronous induction type machines in automotive applications is described. A reconfigurable control scheme is used to provide fault tolerance. The control may operate in one of 3 modes: sensor based indirect field-oriented controls (IFOC), rotor flux estimator (sensorless) based IFOC, and a scalar V/Hz mode.
The operation of the position/speed sensing device is monitored. Position/speed sensors generally have high cost and low reliability. The position sensor presents a single point failure that can cause a loss of propulsion. In the event of a sensor failure, the control system switches to rotor flux estimator (sensorless) based IFOC. The rotor flux estimator based IFOC has limitations at low speeds. Therefore, at low speeds the control system switches over to the lower grade scalar V/Hz type control. The open loop V/Hz type control suffers from poor performance as compared to IFOC controls.